1. Technical Field
The present invention relates to a conveyance device for sheet media stored in a roll, and relates more particularly to a conveyance device that efficiently and desirably brakes a drive gear and conveys the medium accurately with little trouble.
2. Related Art
Receipt printers and other devices that process sheet media (such as paper) stored in a roll have a device for conveying the media to a processing position. The conveyance device usually has an upstream roller that feeds the media from the roll to the conveyance path, and a downstream roller that supplies the fed media to the processing position, and the media is conveyed by driving these rollers. This conveyance device also commonly performs a reversing operation that rotates the medium stored in a roll, and rewinds the conveyed medium to a specific position.
When the conveyance operation ends (stops) and when roll media is manually loaded, inertia can cause the roll medium to rotate too much. This excess rotation can result in unnecessary slack in the medium or the roll medium becoming loose, and as a result can result in a sudden load being applied to the medium when the conveyance operation starts and interfere with accurate media conveyance.
A load is therefore commonly applied to rotation of the roll medium so that the roll does not turn too much.
To address this problem, Japanese Unexamined Patent Appl. Pub. JP-A-2000-327181 describes a roll sheet conveyance device having a spool capable of rotating a sheet roll and a sheet conveyance means that drives sheet conveyance, applies a rotational load to the spool when driving the sheet conveyance means and feeding the sheet from the spool, and prevents the rotational load from acting on the spool when driving the spool to rewind the sheet to the spool.
A device that applies a load as described above, and more specifically a braking device that stops rotation of the roll medium, generally has one brake and is configured to constantly apply a load, or uses an electromagnetic brake. Constantly applying a load means that the conveyance force must be that much greater, which is inefficient in terms of power consumption and requires a larger drive device. When an electromagnetic brake is used, the brake is not applied when the device is turned off, and unwanted rotation of the roll cannot be prevented when the roll medium is loaded by hand, for example.
Variously adjusting brake operation for forward conveyance, reverse conveyance, and at different speeds during the conveyance operation is also not possible when using a single brake as described in JP-A-2000-327181, and controlling brake operation appropriately to different conditions is difficult.